Method of producing elastic thread



Patented Aug. 5, 1952 UNITED STATES PATENT OFFICE A} I neuron-or PROSfiZiiSEhAdTIGTHBEA W i Robert R. Dreisbach, Midland, Mien, assignor to -The Dow Chemical Company, Midland, Mich,

a corporation of Delaware No Drawing. Application August 10,

Serial No. 610,'102- This invention relates to making elastic thread from rubber-like diolefin copolymers.

The production of elastic thread from natural polymerizing the monomers in'approxirnately the following proportions by weight:

Parts rubber by the dry-extrusion of compounded stock is not practical, the extruded filaments being 5 Conjugated diolefin 1.0 non-uniform and very weak, even after curing. Alphaemethyleneealkyl .cyanide 0.15to 1.5

As a result, elastic rubber threadsare made commercially only by complex procedures, such as wet-spinning latex into va. coagulant liquid, or forming rubber sheet and slitting it. (These known processes are summarized, for example, in U. S. Patent 2,338,978.)

It has now been found, however, contrary to experience with natural rubber. that certain rubber-like diolefin copolymers, when compounded, can readily be dry-extruded to form thread which is of excellent uniformity and, after curing, exhibits high strength, good elasticity, and low permanent set.

This finding is the basis of the present invention, which provides a simple method for the production of elastic thread having physical properties approximating or even exceeding those of the natural rubber thread produced by more elaborate processes.

The rubber-like materials to which the new process is applicable are essentially the copolymers of lower aliphatic conjugated diolefins, such as ,butadiene, with alpha-methylene-lower alkyl cyanides, such as vinyl cyanide, with or without lower alkyl alpha-methylene-loweralkyl ketones, e. g. methyl isopropenyl ketone, as third components. In the invention, any of these ccpolymers is mixed with conventional rubber-compounding agents to produce a vulcanizable plastic composition which is dry-extruded through small orifices. The resulting extruded filaments are then cured, as by heating, to form elastic threads.

T e l we a ip a i on u ate diolefin ponent of the copolymers used in the invention is ordinarily butadiene-l.3, although isoprene, Z-ethyl b utadiene-1.3, and 2.3-dimethyl butadiene-1.3 may be substituted for all or a part of it. The. alpha-methylene -lower alkyl cyanide is preferably vinyl cyanide a ry on ril however, iso- Propenyl c n me ee ylonitr le an ot r mater a s thi cla s may e emp oye T e loweralkyl alpha methylene-lower alkyl ketone is preferably methyl isopropenyl ketone, although me h l v ny k t n ethyl yl k tone. met y lpha-et yl-vinyl ke one; is prop v yl k t ne. and t e e a a o operable.

In general, satisfactory elastic threads are obtallied acco din t9 he, nt on. hen. the u eleeri se ce yme s are thes premises b ater-- Alkyl alpha-methylene-alkyl ketone- 0.0 .to 4.0

parts of vinyl cyanidein which the vinyl cyanide does not represent over 35-per cent of the total copolymer. Within this range, optimum results are achieved with 1.25 to 1.6 parts of methyl isop-ropenyl ketone and 0.25 to 1.4 parts of vinyl cyanide per part of butadiene. These copolymers, which have been marketed under the name Thiokol RD, are described in detail in my copending application Serial No. 376,996, filed February 1, 1941, now U. S. Patent No. 2,385,695, to which reference is hereby made.

Another group of operable copolymers are those obtained by polymerizing 1.0 part of butadiene with 0.1 to 0.7 part of vinyl cyanide, the optimum proportions being 0.25 to 0.67 part of the latter. These materials are known commercially by the names Perbunan, Buna N, fHycar OR, Chemigum-N, and l'il-utaprene-N. The basic composition is characterized in. U. S. Patent N .9 3, 0.-

. The rubber-like copolymers used in the invention are prepared by conventional methods, i. e. y polym mixtures of the monomers en mass or in sol ti n, or preferably in an aq ous m lsion, at el va d emperatures, usually below C. Details of the polymerization methods are known in the art and form no, part of the present invention.

.In practice of the invention, a rubber-like diolefin copolymer of the type explained is mixed thoroughly with rubber-compounding agents to form a vulcanizable plastic mass, as by working th ingred ents together on a compounding mill.

In so far as known, any of the compounding.

narily fitted with a die having one or more circular orifices of a diameter below, 0.050 inch, although threads of other cross-sectional shapes may be formed if desired by providing a suitable die. Best results are obtained when the extrusion press has a low inventory and the screw is of the 7 type providing maximum forwarding action with minimum working of the plastic. The compound to be extruded is ordinarily fed to the screw at room temperature, and the temperature of the press is preferably controlled so that the plastic is not heated over 100 to 125 C. at any point. Under these conditions,.extrusion proceeds very smoothly; threads of uniform diameter and excellent appearance are readily produced.

Following extrusion, the thread is cured, usually by heating at an elevated temperature of 100 to 175 C., e. g. about 150 C., for 0.3 to 2 hours, as required. It is preferable during curing to exclude air from contact with the hot thread, as by operating in an atmosphere of inert gas or in vacuum. V

Curing may be effected either by passing the thread as it is extruded through aheated tunnel for a timesufiicient to effect a cure, and then spooling it, or by spooling the thread and curing it'while spooled. In the latter case, it isdesirable to coat the thread with talc or a soap film before spooling to prevent the threads from adhering to one another during the curing step.

After curing, the. thread has considerable strength and high elongation, and is ready for service in most of the applications to which natural rubber thread has been placed.

The extrusion process,'in addition to shaping the rubber compound into thread, imparts added strength thereto, so, that cured thread is frequently found to have from 50 to 100 per cent higher tensile strength than cured test specimens of unextruded stock.

The following examples will further illustrate the invention, but are not to be construed as limiting its scope.

Example 1 'The copolymer used was a "Thiokol RD pro duced by interpolymerization of "1.0 part by weight of butadiene, 1.12 parts of methyl isopropenyl ketone, and 0.37- part of vinyl cyanide in aqueous emulsion. Aweight of 100 parts of this copolymer was compounded on rolls with 40 parts of Gastex furnace black, 5 parts of zinc oxide, 2.5 parts of sulfur, 1 part of mercaptobenzothiazole, 1 part of stearic acid, and parts of dibutyl sebacate.

The resulting vulcanizable plastic composition was forced through a 0.030-inch circular orifice in a diemounted on an extrusion press having a 0.5-inch diameter screw 3.5 inches long operating at 50 R. PJM. The thread'issued at about 8 feet per minute at a temperature of about 90 C.; had a diameter of 0.031 inch, and weighed about.0.008' ounce per foot. It was coated with talc, and spooled'under practically notension. The spools were then inserted in a vacuum oven at 150 C. for 1.0 hour to effect curing.

The resulting elastic thread was smooth-surfaced and of uniform diameter, and exhibited a tensile strength of 5080 pounds per square inch (based on the cross-section of the unstretched used in Example 1.

4 thread) and an elongation at breaking of 520 per cent. Even after aging in air more than two years, the thread retained substantially these original properties.

Example 2 A weight of 100 parts of the copolymer of Example 1 was compounded with 40 parts of Kalvan calcium carbonate, 10 parts of zinc oxide, 2 parts of sulfur, 1 part of mercaptobenzothiaz'ole,

lpart of stearic acid, and 20 parts of dibutyl sebacate. The resulting stock wasextruded and cured as in Example 1. The thread had a diameter of 0.030 inch, a tensile strength of 3300 pounds per square inch, and an elongation of 480 per cent.

Example 3 then extruded and cured as in that example.

The Hycar-OR thread had a tensile strength of 4800 pounds per square inch and an elongation of 420 per cent. The Perbunan thread exhibited a strength of 3750 pounds per square inch and an elongation of 650 per cent.

' mer of a mixture of 1.0 part of a lower aliphatic conjugated diolefin, 0.15 to 1.5 parts of an alphamethylene-lower alkyl cyanide, and 0.0 to 4.0

parts of a lower alkyl alpha-methylene-lo-wer' alkyl ketone, together with rubber-compounding and vulcanizing agents; and curing the resulting extruded thread while preventing it from adhering to like thread during the curing step.

-2. The method of producing a rubber-like elastic thread which comprises: mechanically working at atelevated temperature below C. and dry-extruding through a thread-forming orifice having a diameter below 0.050 inch a vulcanizable plastic composition consisting of a rubber-like copolymer of a mixture of 1.0 part of butadiene, 0.8 to 4.0 parts of methyl isopropenyl ketone, and 0.15 to 1.5'parts of vinyl cyanide, which copolymer contains not more than 35 per cent of combined vinyl cyanide, together with rubber-compounding and vulcanizing agents; and heat-curinglthe resulting extruded thread while preventingit from adhering to like thread during the curing step. 3. A process'according to claim 2 wherein the copolymer is a oopolym'er of 1.0 part of butadiene, 0.25 tolxl parts of vinyl cyanide, and 1.25 to 1.6- parts of methyl isopropenyl ketone.

4. The method of producing a rubber-likeelas tic thread which comprises: mechanically working at an elevatedtemperature below 125 C. and dry-extruding through a thread-forming orifice having a diameter below 0.050 inch a vulcanizalzile' plastic "composition consisting of a rubber-like of these ,copoly-mers was compounded separately with the same agents in the same proportions as were- The resulting stocks were copolymer of a mixture of 1.0 part of butadiene and 0.1 to 0.7 part of vinyl cyanide, together with rubber-compounding and vulcanizing agents; and heat-curing the resulting extruded thread while preventing it from adhering to like thread during the curing step.

5. A process according to claim 4 wherein the copolymer is a copolymer of 1.0 part of butadiene and 0.25 to 0.67 part of vinyl cyanide.

ROBERT R. DREISBACH.

Name Date Number Hartung Feb. 28, 1928 Number Name Date 2,135,395 Holzapfel Nov. 1, 1938 2,149,425 Draemann Mar. 7, 1939 2,156,909 Boyer May 2, 1939 2,170,439 Wiezevich Aug. 22, 1939 2,185,656 Waterman et al. Jan. 2, 1940 2,265,722 De Nie Dec. 9, 1941 2,288,982 Waterman et a1 July 7, 1942 2,233,403 Youker Nov. 2, 1943 10 2,385,695 Dreisbach Sept. 25, 1945 FOREIGN PATENTS Number Country Date 303,867 Great Britain Mar. 13, 1930 OTHER REFERENCES Stocklin: Buna Transactions of Institute of Rubber Industry, 1939, vol. 15, page 63. 

1. THE METHOD OF PRODUCING A RUBBER-LIKE ELASTIC THREAD WHICH COMPRISES: MECHANICALLY WORKING AT AN ELEVATED TEMPERATURE AND DRY-EXTRUDING THROUGH A THREAD-FORMING ORIFICE HAVING A DIMETER BELOW 0.050 INCH A VULCANIZABLE PLASTIC COMPOSITION CONSISTING OF A RUBBER-LIKE COPOLYMER OF A MIXTURE OF 1.0 PART OF A LOWER ALIPHATIC CONJUGATED DIOLEFIN, 0.15 TO 1.5 PARTS OF AN ALPHAMETHYLENE-LOWER ALKYL CYANIDE, AND 0.0 TO 4.0 PARTS OF A LOWER ALKYL ALPHA-METHYLENE-LOWER ALKYL KETONE, TOGETHER WITH RUBBER-COMPOUNDING AND VULCANIZING AGENTS; AND CURING THE RESULTING EXTRUDED THREAD WHILE PREVENTING IT FROM ADHERING TO LIKE THREAD DURING THE CURING STEP. 